Those tumor promoters that are common environmental pollutants and to which humans have a high probability of exposure include the polychlorinated biphenyls (PCBs), phthalic acid esters (PAEs), and chlorinated dibenzo-p-dioxins (TCDD). Well-studied promoters such as the phorbol esters have a wide variety of biochemical effects. By looking for biochemical effects common to the above list of highly diverse compounds, it is hoped that effects relevant to hepatic tumor promotion can be identified. Current studies, which are in a purely exploratory phase, are concentrating on such membrane-related effects as lipid peroxidation and activation of protein kinase C. Lipid peroxidation studies are also directed toward the development of more quantitatively interpretable, in vivo monitoring procedures.